Primula pingbaensis Na Zhang, X.Q.Jiang & Z.K.Wu, a new species of Primulaceae from Gaofeng Mountain of Pingba county, Guizhou, China, is described and illustrated. Morphological evidence supports P. pingbaensis as a member of P. sect. Petiolares on account of scape elongating, pedicels conspicuously thickening in fruit, and its capsule cracking irregularly round the top and crumbling away. Amongst the members of subsect. Davidii, the new species is characterized by having a uniquely smooth leaf blade due to inconspicuously raised veinlets and homostylous flowers with the style usually extending beyond the anthers. The distribution, phenology and conservation status of the new species are also provided.

Guizhou, Karst, new species, ping ba bao chun, Primula sect. Petiolares

Primula L., comprising 521 species mostly found in the temperate zone, is one of the largest genera in Primulaceae (Hu 1994; POWO 2022). More than 300 species of Primula were found in China, and distributed mainly in the southwestern part (Yunnan, Sichuan and Tibet), with the modern diversity center of the genus ranging from the Himalaya-Hengduan mountains chain (Hu 1994; Hu and Kelso 1996; Richards 2003).

In Primula, floral morph (i.e., heterostyly or homostyly) is one of the important characters for species identification. Heterostyly is perhaps the most distinctive feature of Primula (Richards 2003) because most of the species (92%) are heterostylous (Wang et al. 2021). In these species, all the flowers on a plant either have a long style (‘pin morph’) or a short style (‘thrum morph’) differing reciprocally in stigma and anther height. This reciprocal herkogamy is often accompanied by an incompatibility system that makes intermorph crosses more successful than intramorph crosses (Richards 2003). In contrast, the remaining species are almost monomorphic for style condition (i.e., homostylous), having either long styles and long-level stamens (long homostyly) or short styles and short-level stamens (short homostyly). Recently, a novel floral form in Primula was reported by one of the authors (Wu et al. 2023), which is characterized by bell-shaped flowers with exceptionally short tubes, stamens set just above the mouth of the tube and the style either as long as, or exserting, the corolla. In addition, some species have both heterostylous and homostylous populations, such as in P. chungensis Balf.f. & Kingdon-Ward and P. oreodoxa Franch. (Hu 1990).

The Primula sect. Petiolares Pax is well represented in the Himalaya-Hengduan mountains, with only a few members extending into Kashmir, central China, and some other regions (Hu 1990; Hu and Kelso 1996). One of the most important diagnostic characters of the section is that of the capsule being globose, included in the persistent calyx, not opening by valves but crumbling at the membrane apex. More than 60 species of this section are now recognized worldwide (Hu 1994; Hu and Kelso 1996; Hu and Geng 2003; Richards 2003; Li and Hu 2009; Rankin 2010; Hu and Hao 2011; Xu et al. 2014a, 2015, 2016a, 2022a; Ju et al 2018; Yuan et al. 2018).

Guizhou is one of the biodiversity hotspots in China, marked by its karst landscape. According to relevant literatures and Flora of China, there are more than a dozen species of Primula distributed in Guizhou, of which some species are endemic to Guizhou, such as P. esquirolii Petitm. (Wu et al. 2022), P. fangingensis Chen et C.M.Hu, P. kweichouensis W.W.Smith, P. lithophila F.H.Chen & C.M.Hu and P. levicalyx C.M.Hu et Z.R.Xu (Smith et al. 1977; Hu 1990). During the last decade, some newly published Primula species from the adjacent areas were also found within Guizhou, such as P. pelargoniifolia G.Hao, C.M.Hu & Z.Y. Liu (Xu et al. 2014b), P. persimilis G.Hao, C.M.Hu & Y.Xu (Xu et al. 2016b) and P. centellifolia G.Hao, C.M.Hu & Y.Xu (Xu et al. 2017). Recently, a newly described species, namely Primula chishuiensis C.M.Hu, G.Hao & Y.Xu (Xu et al. 2022b) was reported from Guizhou.

Multiple field surveys were carried out from type locality and adjacent areas from 2018 to 2022 to obtain more reliable information on the field distribution of P. esquirolii, species that was last recorded in the 1910s in Pingba county, Guizhou, China. During field surveys in April 2018, we found a Primula, which is suspected to be a member of sect. Petiolares with fruits from Gaofeng mountain in Pingba county. At first, we thought it was P. esquirolii, but different compared to the type specimen of P. esquirolii in its lamina character, where P. esquirolii is conspicuously bullate on the upper surface and strongly honeycombed-reticulate beneath. For further clarification on the identity of the newly collected Primula, the Gaofeng Mountain and adjacent areas were revisited the following years (2019–2022) to observe and collect the plants in flower and fruit. The collected Primula is a slender dwarf perennial herb with smooth, thin papery lamina, bearing homostylous flowers. After comparing the relevant literature for related species, we concluded that this plant was unique and should be described as a new species. Therefore, we describe and illustrate the taxon as new to science here.

The morphological description of the new species was based on living plants from Gaofeng Mountain. For comparison purposes, specimens of closely related species, P. coerulea from Yunnan and P. esquirolii from Guizhou were also collected from their type locality. In addition, specimens’ images online of the closely related species from herbaria P, E, KUN, PE, K, IBSC, and relevant literature (Smith et al. 1977; Hu 1990; Hu and Kelso 1996) were also consulted. All morphological characters of P. pingbaensis and its morphologically similar species in the section Petiolares, including P. esquirolii and P. coerulea, were measured using a vernier calliper. The conservation assessment of the new species was evaluated using the IUCN categories of threat (see IUCN 2012 and IUCN Standards and Petitions Committee 2022).

Most species in the sect. Petiolares of Primula have heterostylous flowers. Only P. hookeri G.Watt, P. chamaethauma W.W.Smith, P. esquirolii and our newly discovered species P. pingbaensis have homostylous flowers. Species with homostylous morphs are usually accompanied by a compatibility system that makes intramorph (and thus self-) crosses more successful (Richards 2003). The selfing homostylous lineages often have a high genetic load, which makes them sensitive to environmental changes and renders population expansion over short periods difficult (Wu et al. 2022). Our observation on Primula species distribution indicated that homostylous species usually have fewer populations or smaller population sizes than closely related heterostylous species. Primula hookeri and P. chamaethauma are distributed in the alpine areas of Yunnan and Tibet (usually over 4000 m a.s.l.) while P. esquirolii and P. pingbaensis occur in the karst areas of Guizhou (usually lower than 1500 m a.s.l.). Field surveys on P. esquirolii showed that it is a species with extremely small populations and was evaluated as‘Critically Endangered’ (Wu et al. 2022), like our new finding of P. pingbaensis.

This study was supported by the National Wild Plant Germplasm Resource Center for Guizhou University of Traditional Chinese Medicine (ZWGX-2015) and Science and Technology Plan Project of Guizhou Province ([2022]-4016). We thank Pro. David Rankin of University of Edinburgh for improving the English of our manuscript, and Ms. XiangLi Wu for the line drawings of the new species.